Phased Arrays - MATLAB Simulations for Radar Systems Design - page 317

then a useful expression for far field is

2 d 2

r ≥ ⁄ λ

(8.15)

Note that far field is a function of both the antenna size and the operating
wavelength.

antenna

A

spherica l
wavefront

δ r

B

r

O

d

r

radiating
source

Figure 8.1. Construction of far field criterion.

8.3. General Arrays

An array is a composite antenna formed from two or more basic radiators.
Each radiator is denoted as an element. The elements forming an array could
be dipoles, dish reflectors, slots in a wave guide, or any other type of radiator.
Array antennas synthesize narrow directive beams that may be steered,
mechanically or electronically, in many directions. Electronic steering is
achieved by controlling the phase of the current feeding the array elements.
Arrays with electronic beam steering capability are called phased arrays.
Phased array antennas, when compared to other simple antennas such as dish
reflectors, are costly and complicated to design. However, the inherent flexibil-
ity of phased array antennas to steer the beam electronically and also the need
for specialized multi-function radar systems have made phased array antennas
attractive for radar applications.